There have been a number of published proposals for the use of detectable changes in quantum tunneling current to measure micro or nano order displacements or motions. For example, Kobayashi et al, have proposed a displacement detector for a micro structure such as an atomic force microscope probe that relies on the extreme sensitivity of a tunneling current to the length of a gap, in the order of 1 nm, between a sample and a sharpened metallic tip. An earlier related disclosure by Kobayashi et al “An integrated tunneling unit” appears in Proceedings of MEMS 1992, Travemünde (Germany), Feb. 4-7, 1992. In an extract entitled “Microsensors get tunnelling” in Design Engineering (Morgan Grampian Ltd, London, U.K.), 1 Nov. 1997, there is a disclosure of an accelerometer that relies on tunnel current effects fabricated in a silicon-on-insulator (S.O.I.) wafer. This device, and a micro-mechanical atomic force sensor head disclosed in European patent publication 262253, rely on the sensitivity of detected quantum tunneling current to the variable width of a gap, typically between a tip and an opposed surface. That is, the tip and surface move towards and away from each other.
Other disclosures of arrangements utilising quantum tunneling between a tip and opposed surface are to be found in U.S. Pat. No. 4,806,755 and international patent publication WO 97/20189.
The present applicant's prior international patent publication WO 00/14476 discloses micromechanical apparatus for measuring or monitoring the relative position or displacement of two elements in which a pair of elongate electrical conductors are disposed at a mutual separation such that, on application of an electrical potential difference across the conductors, there is a detectable quantum tunneling current between the conductors. This device is sensitive to the degree of alignment, either lateral or angular, between the opposed conductors. In one form of the device, respective substrates mount opposed arrays of conductors at a spacing in the range 2 to 100 angstroms. Disclosed arrangements for accurately maintaining this gap include the use of C60 nanobearings or a separation film of an organic medium such as cyclohexane.
The concepts and structures disclosed in WO 00/14476 have great promise for a wide variety of applications at micro and nano level. It is an object of the present invention to provide a class of practical devices embodying those concepts.